Effect of major impurities in crude glycerol on solubility and properties of glycerol/methanol/bio-oil blends

Abstract

This study investigates the effect of major impurities in crude glycerol (water, soap, NaCl and NaOH) on the solubility and fuel properties of glycerol/methanol/bio-oil blends. All the impurities considered are found to worsen the solubility of glycerol in the bio-oil to some degree. The effect of water and soap on glycerol solubility in the bio-oil only becomes significant when the water to bio-oil ratio or the soap to bio-oil ratio exceeds 0.3 and 0.01, respectively. However, salt (NaCl) and alkaline catalyst (NaOH) can severely worsen the solubility of glycerol in the bio-oil even at a concentration of 2% in the glycerol aqueous solutions. Compared to solubility, the rheological properties and fuel properties (including heating value, surface tension, density, etc.) of the glycerol/methanol/bio-oil blends are little influenced by these impurities, except the acidity being slightly reduced for fuel blends containing high content of NaOH (e.g. 10% of NaOH in aqueous glycerol solution). The impurities also have appreciable effect on the ageing of the composed fuel blends. In presence of alkaline matter (soap or NaOH), the changes in fuel properties (viscosity, water content and especially acidity) due to ageing become slightly less. Further investigations on solubility of formulated crude glycerol (FCG) in the bio-oil and properties of the FCG/methanol/bio-oil blends suggest that the crude-glycerol/bio-oil blends production process can be potentially integrated into the existing biodiesel production process.